The present invention relates to gas measurement for constituent concentration and flow rate emitted from processes such as burning coal, oil, gas, wood, sewage, hazardous wastes, or venting from noncombustion processes.
The United States Environmental Protection Agency (EPA) has regulated techniques including reference methods for the measurement of gas constituent concentrations and flow from various processes. These techniques are found in Title 40 of the Code of Federal Regulations. The regulations detail the method to perform testing and report the results. This allows the emissions to be compared on an equal basis between different locations in the U.S. and among various industries.
Among the procedures to be followed are the measurement of pollutants for a volume of emitted gas at standard conditions. Briefly, standard conditions are determined by the gas flow temperature, "zero flow" pressure, atmospheric pressure, and calculated (average) molecular weight for the constituents to be measured. Also, a sample maintained at a temperature above the dew point of the relevant gases is required for determination of moisture content.
The devices used in sample collection must be chemically inert with respect to the sampled gases to ensure accuracy. The concern of the EPA is the mass quantity of an emitted gas and not the relative percentage in the total emission.
EPA regulations are included for both continuous emissions monitoring (CEM) and relative accuracy test auditing (RATA). CEMs are permanent, usually stationary instrument systems. RATA is a federally mandated, annual procedure to ensure the accuracy of the CEM reporting and is often conducted by a contracting service. The RATA testing is typically a lengthy process with a number of test procedures involving manual steps, with data from the tests subsequently input into a computer to generate an official report.
The recent enactment of the "Clean Air Act Amendments of 1990" has resulted in regulations that have increased the number of site emission sources requiring testing services. Currently, the available personnel to support these activities is critically low, and therefore emissions reporting is often delayed.
The typical RATA test requires 12 hours and a 3-person team. This team must climb to the test ports, which for a typical industrial smoke stack is located 100-500 feet above the ground. For power utilities, the smoke stack may be up to 46 feet in diameter; although, they are typically of 20-25 feet in diameter. The testing is conducted at 4 ports around the smoke stack, at a total of 24 radial traverse points within the smoke stack. These points are the centroids of 24 sites of equal area. The numerous gas sample collections and flow measurements require the team to repeatedly install and calibrate the devices, as well as perform leak checks and the necessary instrument purging between each traverse.
Recent advancements in testing techniques have allowed automation of some of these tasks and thus simplify the test procedures somewhat. For example, United Sciences, Inc., of Gibsonia, Pa., has designed a motorized, telescoping probe that automatically measures and records a velocity pressure at a specified traverse point in a smoke stack or exhaust duct. The probe has a reach or extension limited to 12 feet, and has a cost of several tens of thousands of dollars.
However, the numerous other gas measurements, and their leak checks and calibrations, must still be done manually. The operators are still required to manually reposition the single probe at each of the four ports of testing, as well as manually purge the probe between the pressure measurements.